Effects of total dissolved gas supersaturated water on lethality and catalase activity of Chinese sucker(Myxocyprinus asiaticus Bleeker)

Total dissolved gas(TDG) supersaturation caused by dam sluicing can result in gas bubble trauma(GBT) in fish and threaten their survival.In the present study,Chinese suckers(Myxocyprinus asiaticus Bleeker) were exposed to TDG supersaturated water at levels ranging from 120% to 145% for 48 h.The median lethal concentration(LC 50) and the median lethal time(LT 50) were determined to evaluate acute lethal effects on Chinese suckers.The results showed that the LC 50 values of 4,6,8,and 10 h were 142%,137%,135%,and 130%,respectively.The LT 50 values were 3.2,4.7,7.8,9.2,and 43.4 h,respectively,when TDG supersaturated levels were 145%,140%,135%,130%,and 125%.Furthermore,the biological responses in Chinese suckers were studied by assaying the catalase(CAT) activities in gills and muscles at the supersaturation level of 140% within LT 50.The CAT activities in the gills and muscle tissues exhibited a regularity of a decrease after an increase.CAT activities in the muscles were increased significantly at 3/5LT 50(P<0.05) and then came back to the normal level.However,there were no significant differences between the treatment group(TDG level of 140%) and the control group(TDG level of 100%) on CAT activities in the gills before 3/5LT 50(P>0.05),but the activities were significantly lower than the normal level at 4/5LT 50 and LT 50(P<0.05).

Improved genome assembly of Chinese sucker(Myxocyprinus asiaticus)provides insights into the identification and characterization of pharyngeal teeth related maker genes in Cyprinoidei

The Chinese sucker,Myxocyprinus asiaticus(M.asiaticus,Catostomidae,Cypriniformes),is the only living species of Catostomidae in Asia.There are more than 75 species of this family in North America.The fossil record of this group dates back to the early Eocene.As the Chinese sucker is located at the base of the Cyprinoidei phylogeny,this species is also important in clarifying the evolutionary relationships within Cyprinoidei.Here,we assembled a high-quality genome of the Chinese sucker,contig N50(40.26 Mb),which is nearly ten times longer than the previous version(4.19 Mb).Phylogenetic analysis identified that Chinese sucker together with Cyprinidae groups are paraphyletic with respect to Cobitoidea.The specific whole genome duplication event of the Chinese sucker was estimated to have occurred~25.9 million years ago.Analysis of population historical changes indicated a trend of reduction for the Chinese sucker and T.tibetana.Since Dlx genes play a key role in Cypriniformes pharyngeal teeth development,we conducted a genome-wide identification of Dlx genes,and found that these genes were doubled in whole genome duplication events,followed by the loss of specific copies.Transcriptome results showed that the expression levels of these paralogous genes were similar.This genomic resource provides useful information for the protection of Chinese sucker and functional study of Dlx genes.